1. Field of the Invention
This invention relates to electronic detonator delay circuits.
2. Related Art
Electronic circuits for firing electrical initiation elements within detonators after a predetermined, electronically-controlled delay period are known. The delay period is measured from the receipt of a non-electric initiation signal which may also provide power for the timer circuit and for the initiation element. Thus, U.S. Pat. No. 5,133,257 to Jonsson, issued Jul. 28, 1992, discloses an ignition system comprising a piezoelectric transducer that can be disposed next to a detonating cord branch line. When the detonating cord detonates, it releases energy in the form of a shock wave, which induces the transducer to produce an electrical pulse. The electrical energy from the transducer is stored in a capacitor which provides power for a timer. After a predetermined delay, the timer allows the remaining stored energy in the capacitor to fire an ignition head in the detonator. The ignition head initiates explosive material, thus providing the explosive output for the detonator. Similar arrangements are seen in U.S. Pat. No. 5,173,569 to Pallanck et al, issued Dec. 22, 1992; in U.S. Pat. No. 5,377,592 to Rode et al, issued Jan. 3, 1995 (which teaches the use of a 3 microfarad (.mu.f) storage capacitor rated at 35 volts) (see column 7, lines 11-15); and in U.S. Pat. No. 5,435,248 to Rode et al, issued Jul. 25, 1995. As taught in U.S. Pat. No. 5,435,248 at column 9, lines 41-50, the electronic circuits of such detonators are typically formed in a single integrated circuit ("IC") manufactured by a complementary metal oxide semiconductor ("CMOS") process used in conjunction with a 10 .mu.f storage capacitor (rated at 35 volts) (see column 6, lines 45-52). CMOS circuitry is characterized by its low power consumption and low heat dissipation.
Semiconductor bridge ("SCB") igniters are known in the art, as disclosed in U.S. Pat. No. 4,708,060 to Bickes, Jr. et al, issued Nov. 24, 1987, which exemplifies the use of aluminum for the metallized pads of the SCB. Semiconductor bridge igniters utilizing tungsten for the metallized pads are also known, as disclosed in U.S. Pat. No. 4,976,200 to Benson et al, issued Dec. 11, 1990. Such devices generally have impedances of less than 10 ohms, e.g., about 1 ohm.